(1) Field of the Invention
The present invention relates to improvements in ion implantation apparatus used in the manufacture of integrated circuit semiconductor devices, more particularly to an improved mechanism for moving the shutter used to control the ion beam in the apparatus.
(2) Description of the Prior Art
The basic elements of an ion implantation apparatus are illustrated in FIG. 1. An ion source 10 provides suitable impurity ions, which are accelerated from the source 10 by a magnetic field 12 into a beam 13 that enters tube 14. Beam shaping plates 16 shape the beam to provide a uniform dispersion of ions. The ions are subsequently implanted into semiconductor wafer 18. A shutter 20 controls the ion beam exposure of the wafer 18 by either shutting off the beam or allowing it to proceed to the wafer. The elements are mounted in chamber 22.
A known mechanism for rotating shutter 20 is illustrated in FIG. 2. The shutter 20 is mounted on rotatable shaft 24. Cross bar 26 is fixed to shaft 24. An abutment means is provided to limit the rotational movement of bar 26, shaft 24, and shutter 20. A cam 28 can be used as an adjustable abutment by rotating it about axis 30 until the cam surface is in the proper position to provide the desired stop for cross bar 26. An actuating one-way solenoid 32 having a push rod 34 and a return spring 36 is used to rotate shutter 20. A bifurcated element 38, provided with a steel pin 40, is affixed to push rod 34, as shown. A link 42 with a bifurcated end 44 is connected to the bifurcated element 38 by pin 40 to provide a articulated connection between cross bar 26 and push rod 34. Link 42 is joined to cross bar 26 with steel pin 46.
In operation the pins 40 and 46 are subjected to high impact forces, particularly when the cross bar strikes the abutment cam surface. This results in very significant sheer forces and wear since the shutter must be opened very frequently. The sheer force is so high that the pins may be cut off. As the linkage is operated, both the pins and the apertures are subject to wear resulting in loosely fitting pins. This looseness in turn compounds the sheer actions on the pins resulting in premature failure. In a typical failure, the pin 40 would be cut off by the sheer force. A failure of the linkage will result in inappropriate implanted ion concentrations in the wafer in the apparatus, and possibly more wafers if the failure is not noticed immediately. Further, even looseness of the linkage without a catastrophic failure could alter the amount of ions that are implanted, resulting in ruined product, or product of lower quality.